The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Continuously variable transmissions provide smooth, stepless power transfer to the final drive assembly of a motor vehicle. They are thus attractive to drivers not only because they eliminate conventional gear shifts but also because they are capable of closely matching the engine speed and torque to the vehicle load thereby improving both performance and fuel economy.
They are not without drawbacks, however, the most significant generally being their somewhat limited input to output speed ratio range. Whereas a multiple gear (conventional) transmission can be equipped with any number of forward gears, commonly now, six, seven or eight, to provide any desired input to output ratio range, continuously variable transmissions do not generally enjoy this open ended capability.
Accordingly, in many applications, a basic continuously variable device such as a variator is teamed with one or more gear trains and engagement (selection) devices such as clutches to provide one or more additional speed (gear) ratios to augment the speed ratio range of the variator. A consequence of such additional transmission components is that whereas the output of the variator is smooth and shiftless, an operational feel to which the vehicle operator becomes accustomed, such additional shift components often provide dramatic ratio changes while the variator adjusts or resets from a low ratio (high speed range) to a high ratio (low speed range). Such ratio changes are difficult to achieve without an interruption of torque delivery to the final drive assembly and thus difficult to achieve without being sensed by the driver and passengers.
The present invention is directed to solving this problem and providing smooth and virtually undetectable mode shifts in a multiple mode continuously variable transmission.